Single-site catalysts can be divided into metallocenes and non-metallocenes. Metallocene single-site catalysts are those which comprise transition metal complexes of cyclopentadienyl (Cp) or Cp derivative ligands. Non-metallocene single-site catalysts are often referred to those having one or more non-Cp, heteroatomic ligands, such as boraaryl, pyrrolyl, azaborolinyl, indenoindolyl, and quinolinyl ligands.
Single-site catalysts are generally homogeneous and soluble in olefins and most solvents. While these catalysts are most suitable for solution polymerizations, they need to be supported for use in the heterogeneous polymerization processes, including slurry and gas phase processes. Supporting single-site catalysts offer many challenges because of their high solubility. When a single-site catalyst is merely coated on or impregnated in an inorganic or polymer support, it tends to release from the support. This often causes many problems in slurry and gas phase polymerization, for example, reactor fouling, poor catalytic activity, low polymer bulk density, and poor polymer particle morphology.
To overcome the problems, many attempts have been made to chemically bond single-site catalysts to polymer supports. For instance, U.S. Pat. No. 5,492,985 teaches polystyrene bound single-site catalysts. Preparation of the polystyrene bound single-site catalysts involves a series of difficult reactions: forming chloromethylated polystyrene from polystyrene; forming methylpolystyrenecyclopentadiene by the reaction of chloromethylated polystyrene with cyclopentadienylsodium; forming lithiated methylpolystyrenecyclopentadiene by the reaction of n-butyllithium with methylpolystyrenecyclopentadiene; and then forming transition metal complex from the lithiated methylpolystyrenecyclopentadiene. This preparation is rather complex and costly.
It is apparent that new polymer bound single-site catalysts are needed. Ideally, the catalysts would be easy to prepare and remain high activity.